Transformer for longwire antennas to reduce noise problem?
 

Hey -

I posted in here recently about active shortwave antennas - well, I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem,
however - so bad that I can't hear stations on 20 meters! There's a
pretty solid S9 noise floor that prevents me from hearing anything
other than WWV and the major broadcast stations. Now, I know I can do
better with the amount of wire I've got strung out there.

I was thinking about adding one of those 9:1 transformers or other
impedance matching things for longwires; would this reduce the noise
problem I'm having? Any other tips for reducing longwire noise? It
works enough, but I know I can do better...


Thanks in advance.

In article ,
(TheGnome) wrote:

Hey -

I posted in here recently about active shortwave antennas - well, I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem,
however - so bad that I can't hear stations on 20 meters! There's a
pretty solid S9 noise floor that prevents me from hearing anything
other than WWV and the major broadcast stations. Now, I know I can do
better with the amount of wire I've got strung out there.

I was thinking about adding one of those 9:1 transformers or other
impedance matching things for longwires; would this reduce the noise
problem I'm having? Any other tips for reducing longwire noise? It
works enough, but I know I can do better...


Thanks in advance.

You are in a tough spot with all the computers and other electronics
around. A common mode antenna is the worst choice for you as the S9
noise floor attests.

A small active loop in the quietest spot in your room or on the roof if
you manage it would work the best. I would be surprised if a transformer
would help you much on the wire because I expect that the antenna itself
is picking up the majority of the noise. An exception to this would be
if that 75 feet of wire on the perpendicular roof is a garage and not
other rooms full of computer equipment.

--
Telamon
Ventura, California

On 26 Sep 2004 14:55:49 -0700, (TheGnome)
wrote:

I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem

Hi OM,

Use coax out 25-30 of those 75 feet. At the far end, put your
counterpoise there and thus move your input to a position remote from
that same noise (presumably in your room). At that same far end, add
a 1:1 BalUn or W2DU style otherwise known as a Current BalUn rather
than a Voltage BalUn (the distinction in this regard is important).
This will keep noise from coupling to the outside of your coax and
funneling into the feedpoint (as long as your receiver has good
shielding). It is called "choking." This will help with radiative,
local noise. You can add a second BalUn on the antenna/counterpoise
side for Z transformation, if you choose.

If the noise is conductive, then it is coming in through your power
supply (AC is carrying trash). Good ground can help solve this,
unless you are in a room on a high floor. You can confirm conductive
noise by breaking all AC and ground paths and running on battery power
(if this is an option) or connecting your antenna to a battery powered
receiver. Another option (if no battery options are available) is to
get a long extension cord and try another outlet that you can identify
as being on a separate breaker (this may not be easy in a dorm
situation). With this, you may find a quiet AC branch that is not
shared with the noise generators.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On 26 Sep 2004 14:55:49 -0700, (TheGnome)
wrote:

I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem

Hi OM,

Use coax out 25-30 of those 75 feet. At the far end, put your
counterpoise there and thus move your input to a position remote from
that same noise (presumably in your room). At that same far end, add
a 1:1 BalUn or W2DU style otherwise known as a Current BalUn rather
than a Voltage BalUn (the distinction in this regard is important).
This will keep noise from coupling to the outside of your coax and
funneling into the feedpoint (as long as your receiver has good
shielding). It is called "choking." This will help with radiative,
local noise. You can add a second BalUn on the antenna/counterpoise
side for Z transformation, if you choose.

If the noise is conductive, then it is coming in through your power
supply (AC is carrying trash). Good ground can help solve this,
unless you are in a room on a high floor. You can confirm conductive
noise by breaking all AC and ground paths and running on battery power
(if this is an option) or connecting your antenna to a battery powered
receiver. Another option (if no battery options are available) is to
get a long extension cord and try another outlet that you can identify
as being on a separate breaker (this may not be easy in a dorm
situation). With this, you may find a quiet AC branch that is not
shared with the noise generators.

73's
Richard Clark, KB7QHC

I agree with Richard.

The problem with outside antennas and noise often results from the
noise being carried common-mode on the outside of the cable
braid BACK to the antenna. Use a decoupling choke at the
antenna end of the coax. The 9:1 balun or transformer will
minimize losses due to high impedance swings at certain
frequencies--it won't do much for noise however.

Pete

In article MHI5d.301695$Lj.294959@fed1read03,
" Uncle Peter" wrote:

"Richard Clark" wrote in message
...
On 26 Sep 2004 14:55:49 -0700, (TheGnome)
wrote:

I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem

Hi OM,

Use coax out 25-30 of those 75 feet. At the far end, put your
counterpoise there and thus move your input to a position remote from
that same noise (presumably in your room). At that same far end, add
a 1:1 BalUn or W2DU style otherwise known as a Current BalUn rather
than a Voltage BalUn (the distinction in this regard is important).
This will keep noise from coupling to the outside of your coax and
funneling into the feedpoint (as long as your receiver has good
shielding). It is called "choking." This will help with radiative,
local noise. You can add a second BalUn on the antenna/counterpoise
side for Z transformation, if you choose.

If the noise is conductive, then it is coming in through your power
supply (AC is carrying trash). Good ground can help solve this,
unless you are in a room on a high floor. You can confirm conductive
noise by breaking all AC and ground paths and running on battery power
(if this is an option) or connecting your antenna to a battery powered
receiver. Another option (if no battery options are available) is to
get a long extension cord and try another outlet that you can identify
as being on a separate breaker (this may not be easy in a dorm
situation). With this, you may find a quiet AC branch that is not
shared with the noise generators.

73's
Richard Clark, KB7QHC

I agree with Richard.

The problem with outside antennas and noise often results from the
noise being carried common-mode on the outside of the cable
braid BACK to the antenna. Use a decoupling choke at the
antenna end of the coax. The 9:1 balun or transformer will
minimize losses due to high impedance swings at certain
frequencies--it won't do much for noise however.


Please don't cross post into rec.radio.amateur.antenna. Those guys are
bad enough there and who wants to read them in this newsgroup.

--
Telamon
Ventura, California

The only thing that will help is to get the antenna (and counterpoise) out
of the noise.
"TheGnome" wrote in message
om...
Hey -

I posted in here recently about active shortwave antennas - well, I
managed to get 75 feet of #26 magnet wire on a perpendicular roof to
my window of my dorm room, and two runs of 15' speaker wire as a
counterpoise in my room. I'm getting a really bad noise problem,
however - so bad that I can't hear stations on 20 meters! There's a
pretty solid S9 noise floor that prevents me from hearing anything
other than WWV and the major broadcast stations. Now, I know I can do
better with the amount of wire I've got strung out there.

I was thinking about adding one of those 9:1 transformers or other
impedance matching things for longwires; would this reduce the noise
problem I'm having? Any other tips for reducing longwire noise? It
works enough, but I know I can do better...


Thanks in advance.

In article ,
(TheGnome) wrote:

I was thinking about adding one of those 9:1 transformers or other
impedance matching things for longwires; would this reduce the noise
problem I'm having? Any other tips for reducing longwire noise? It
works enough, but I know I can do better...

I had a noise problem with a longwire. I got a 4:1 balun from LDG, it's
meant to be used with their autotuners, bit also can be used by itself.

On the high impedance side of the balun, one side goes to the antenna,
and the other side to ground. You then use coax to connect to your
receiver. I mounted the balun on the wall right where the antenna
leaves the house, and connected the ground terminal to a ground rod
directly below that point.

The reduction in noise was dramatic! This tells me that what you
propose should work for you, as long as you can connect one side of the
high-impedance side to a good ground. In a dorm room, I don't know if
you have a decent RF ground available, depends on the circumstances of
the plumbing, etc.

If the balun is not too expensive, it is probably worth your while to
get one and to experiment. Try yo buy one from a place with a liberal
return policy, in case it does not work for you.

Good luck!

73 de KC1IH

--
Larry Weil
Lake Wobegone, NH